4 * Copyright (C) 1994-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
8 * This file contains decompression data source routines for the case of
9 * reading JPEG data from a file (or any stdio stream). While these routines
10 * are sufficient for most applications, some will want to use a different
12 * IMPORTANT: we assume that fread() will correctly transcribe an array of
13 * JOCTETs from 8-bit-wide elements on external storage. If char is wider
14 * than 8 bits on your machine, you may need to do some tweaking.
17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
19 /* Expanded data source object for stdio input */
22 struct jpeg_source_mgr pub; /* public fields */
24 std::ifstream *infile; /* source stream */
25 JOCTET * buffer; /* start of buffer */
26 boolean start_of_file; /* have we gotten any data yet? */
28 gdcm::JPEGFragment *frag;
32 typedef my_source_mgr * my_src_ptr;
34 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
38 * Initialize source --- called by jpeg_read_header
39 * before any data is actually read.
43 init_source (j_decompress_ptr cinfo)
45 my_src_ptr src = (my_src_ptr) cinfo->src;
47 /* We reset the empty-input-file flag for each image,
48 * but we don't clear the input buffer.
49 * This is correct behavior for reading a series of images from one source.
51 src->start_of_file = TRUE;
56 * Fill the input buffer --- called whenever buffer is emptied.
58 * In typical applications, this should read fresh data into the buffer
59 * (ignoring the current state of next_input_byte & bytes_in_buffer),
60 * reset the pointer & count to the start of the buffer, and return TRUE
61 * indicating that the buffer has been reloaded. It is not necessary to
62 * fill the buffer entirely, only to obtain at least one more byte.
64 * There is no such thing as an EOF return. If the end of the file has been
65 * reached, the routine has a choice of ERREXIT() or inserting fake data into
66 * the buffer. In most cases, generating a warning message and inserting a
67 * fake EOI marker is the best course of action --- this will allow the
68 * decompressor to output however much of the image is there. However,
69 * the resulting error message is misleading if the real problem is an empty
70 * input file, so we handle that case specially.
72 * In applications that need to be able to suspend compression due to input
73 * not being available yet, a FALSE return indicates that no more data can be
74 * obtained right now, but more may be forthcoming later. In this situation,
75 * the decompressor will return to its caller (with an indication of the
76 * number of scanlines it has read, if any). The application should resume
77 * decompression after it has loaded more data into the input buffer. Note
78 * that there are substantial restrictions on the use of suspension --- see
81 * When suspending, the decompressor will back up to a convenient restart point
82 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
83 * indicate where the restart point will be if the current call returns FALSE.
84 * Data beyond this point must be rescanned after resumption, so move it to
85 * the front of the buffer rather than discarding it.
89 fill_input_buffer (j_decompress_ptr cinfo)
91 my_src_ptr src = (my_src_ptr) cinfo->src;
93 if( src->bytes_read == src->frag->GetLength() )
95 // Start the I/O suspension simply by returning false here:
99 size_t input_buf_size = INPUT_BUF_SIZE;
100 if( (src->bytes_read + INPUT_BUF_SIZE) > src->frag->GetLength() )
102 input_buf_size = src->frag->GetLength() - src->bytes_read;
105 src->infile->read( (char*)src->buffer, input_buf_size);
106 size_t nbytes = src->infile->gcount();
109 if (src->start_of_file) /* Treat empty input file as fatal error */
110 ERREXIT(cinfo, JERR_INPUT_EMPTY);
111 WARNMS(cinfo, JWRN_JPEG_EOF);
112 /* Insert a fake EOI marker */
113 src->buffer[0] = (JOCTET) 0xFF;
114 src->buffer[1] = (JOCTET) JPEG_EOI;
118 src->pub.next_input_byte = src->buffer;
119 src->pub.bytes_in_buffer = nbytes;
120 src->start_of_file = FALSE;
121 src->bytes_read += nbytes;
128 * Skip data --- used to skip over a potentially large amount of
129 * uninteresting data (such as an APPn marker).
131 * Writers of suspendable-input applications must note that skip_input_data
132 * is not granted the right to give a suspension return. If the skip extends
133 * beyond the data currently in the buffer, the buffer can be marked empty so
134 * that the next read will cause a fill_input_buffer call that can suspend.
135 * Arranging for additional bytes to be discarded before reloading the input
136 * buffer is the application writer's problem.
140 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
142 my_src_ptr src = (my_src_ptr) cinfo->src;
144 /* Just a dumb implementation for now. Could use fseek() except
145 * it doesn't work on pipes. Not clear that being smart is worth
146 * any trouble anyway --- large skips are infrequent.
149 while (num_bytes > (long) src->pub.bytes_in_buffer) {
150 num_bytes -= (long) src->pub.bytes_in_buffer;
151 (void) fill_input_buffer(cinfo);
152 /* note we assume that fill_input_buffer will never return FALSE,
153 * so suspension need not be handled.
156 src->pub.next_input_byte += (size_t) num_bytes;
157 src->pub.bytes_in_buffer -= (size_t) num_bytes;
163 * An additional method that can be provided by data source modules is the
164 * resync_to_restart method for error recovery in the presence of RST markers.
165 * For the moment, this source module just uses the default resync method
166 * provided by the JPEG library. That method assumes that no backtracking
172 * Terminate source --- called by jpeg_finish_decompress
173 * after all data has been read. Often a no-op.
175 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
176 * application must deal with any cleanup that should happen even
181 term_source (j_decompress_ptr cinfo)
184 /* no work necessary here */
189 * Prepare for input from a stdio stream.
190 * The caller must have already opened the stream, and is responsible
191 * for closing it after finishing decompression.
195 jpeg_stdio_src (j_decompress_ptr cinfo, std::ifstream * infile, gdcm::JPEGFragment *frag, int flag)
199 /* The source object and input buffer are made permanent so that a series
200 * of JPEG images can be read from the same file by calling jpeg_stdio_src
201 * only before the first one. (If we discarded the buffer at the end of
202 * one image, we'd likely lose the start of the next one.)
203 * This makes it unsafe to use this manager and a different source
204 * manager serially with the same JPEG object. Caveat programmer.
206 if (cinfo->src == NULL) { /* first time for this JPEG object? */
207 cinfo->src = (struct jpeg_source_mgr *)
208 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
209 SIZEOF(my_source_mgr));
210 src = (my_src_ptr) cinfo->src;
211 src->buffer = (JOCTET *)
212 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
213 INPUT_BUF_SIZE * SIZEOF(JOCTET));
216 src = (my_src_ptr) cinfo->src;
217 src->pub.init_source = init_source;
218 src->pub.fill_input_buffer = fill_input_buffer;
219 src->pub.skip_input_data = skip_input_data;
220 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
221 src->pub.term_source = term_source;
222 src->infile = infile;
224 // Need to setup a new buffer, clean bytes_in_buffer and next_input_byte
227 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
228 src->pub.next_input_byte = NULL; /* until buffer loaded */
230 //only upate the new fragment, valid for both 'flag' value